The present invention relates to a method for detecting and correcting pulse noise in a multifunctional remote control transmitter, and particularly to a method for detecting and correcting noise caused by internal factors such as the intensity of the infrared signal or such external factors as an incandescent or fluorescent lamp, in a waveform analyzing device for pulse-phase modulated (PPM) signals, e.g., a multifunctional remote control transmitter or similar device.
FIG. 1 illustrates the construction of a conventional PPM waveform analyzing device. Referring to FIG. 1, a light receiver 1 receives a PPM signal from an outside source, and in turn provides the input to a waveform amplifier 2 which amplifies and then transmits the PPM signal to an input terminal LOAD of a counter 3, a carrier count terminal A and a first interrupt terminal INT1 of a microprocessor 5. The PPM signal input to the LOAD terminal of counter 3 is counted in accordance with the clock signal applied to the clock terminal of counter 3 from a clock generator 4, and is transmitted to a second interrupt terminal INT2 of microprocessor 5 via an output terminal Qn of counter 3. The PPM signal entering light receiver 1 is either a type of signal that does not include a carrier as shown in FIG. 2Aa, or includes a carrier as shown in FIG. 3Aa. However, in practical applications, the signal which enters light receiver 1 and passes through waveform amplifier 2 will include noise as in FIGS. 2Ab and 3Ab showing noisy PPM signals (with and without the carrier respectively) caused by the internal or external factors. Accordingly, the signal fed to the first interrupt terminal INT1 of microprocessor 5 includes the above noise as shown in FIGS. 2Ab and 3Ab. Microprocessor 5 receives the waveform shown in either FIGS. 2Ab or FIG. 3Ab via carrier count terminal A, and counts the number of carrier pulses in a waveform as shown in FIG. 3Ab if the carrier is present.
FIGS. 2Ac and 3Ac illustrate the waveforms of the signal which is transmitted from output terminal Qn of counter 3 to second interrupt terminal INT2 of microprocessor 5 and includes noise. As described above, the external environment or such internal factors as the intensity of the infrared remote control signal from the external source, causes noise to occur and accordingly an inaccurate remote control signal to be input to light receiver 1, creating malfunctions.
A reconfigurable remote control transmitter which inputs a multiple of remote control signals to a single transmitter, and disclosed in U.S. Pat. No. 4,623,887, provides for at least two inputs and comparisons of the remote control signal, in order to assist in the detection and correction of the noise included in the received signals. However, it is unable to completely eliminate the noise.